In a known closed pressure type kneader for kneading a high viscosity kneading material such as rubber, plastic and ceramics, temperature of the kneading material which generate heat during a kneading operation is measured, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2012-21817, by providing a temperature detection end of the thermocouple temperature detector to extend from the bottom or side wall of the kneading tank for sensing the temperature of the kneading material which comes into contact with the temperature detection end. In kneaders having twin-shaft type kneading rotors which engagingly rotate in the kneading tank, lumpy or granular organic polymer materials having high viscosity is kneaded with compounding agent of inorganic substances having abrasiveness. Accordingly, a heavy rotation load is applied on the kneading material from the rotating kneading rotors of twin-shaft type, and a pressure load of the pressure lid is applied on the kneading material in order to prevent the kneading material from being uplifted in the kneading tank. The heat sensing section of the thermocouple element which is disposed on the temperature detection end of the thermocouple temperature detector is, therefore, housed in a protective tube made of a rigid material having a strength with abrasion resistance and impact resistance and is mounted on the bottom or side wall of the kneading tank.
In the thermocouple element housed in the above-described protective tube, the temperature of the kneading material which varies according to the progress of kneading is transferred to the thermocouple element via the protective tube. Accordingly, in order to allow the measured temperature to follow the temperature change of the measurement target with high sensitivity, a grounding type is effective in which the distal end of the thermocouple element is welded to the distal end of the protective tube so that the temperature of the measurement target can be sensed by the outer surface of the protective tube and electromotive force generated by the thermocouple element is transmitted to a temperature display via a conductive wire. In this case, when the strength of the protective tube for bearing a load applied from the measurement target is sufficiently increased, the heat capacity of the protective tube increases. As a consequence, the thermocouple element does not always directly sense the temperature of the kneading material and is largely controlled by the temperature of the protective tube itself, and fails to follow the temperature change of the kneading material with high sensitivity.
Further, when a rubber compound is kneaded in the kneading tank of the closed pressure type kneader, a loading rate of the kneading material including a compound agent to the kneading tank is 70 to 80% of the volume of the kneading tank to provide a flowing space for the kneading material in order to facilitate uniform distribution of the kneading material. Accordingly, the kneading material is not constantly in close contact with the detection end of the thermocouple temperature detector and is brought into contact with and moved away from the heat sensing section of the temperature detection end by engaging rotation of the twin-shaft type kneading rotors so as to dynamically moves in the flow space in the kneading tank not only in the rotation direction but also in the axis direction of the kneading rotor. As a consequence, the kneading material repeatedly comes into instantaneous contact with the temperature detection end, and the detection end fails to precisely sense the temperature of the kneading material during kneading without having a highly sensitive ability to follow the temperature.
In spite of the recent high level of industrial technology, the closed pressure type kneader for high viscosity kneading material fails to display precise temperature values on the instrument due to the above problems and in most cases, displays only the measurement value which is lower than the actual temperature. This may be one of the causes of failure of preventing the variation of plasticity, which is one of the quality properties in a rubber kneading material of a small batch size. Further, the difference between the measured temperature and the actual temperature of the kneading material sacrifices recognition of the precise terminating point of kneading by temperature and precise temperature control automatic kneading which terminates kneading by setting the upper limit temperature.
In order to overcome the above problems, in the thermocouple temperature detector disclosed in Japanese Unexamined Patent Application Publication No. 2012-21817, the shape and configuration of the protective tube which encloses the thermocouple element is improved so as to increase the sensitivity in an attempt to improve the accuracy of measured temperature. Since the protruding length of the detection end which protrudes into the kneading tank is formed large so that the thermocouple temperature detector does not lose heat sensitivity, a strength that can resist bending and breaking of the protective tube needs to be kept. As a result, the heat capacity of the protective tube increases, and the heat accumulation temperature effects to the measured temperature. This is not desirable for a parameter of kneading management.
Further, in recent years, a high speed rotation rotor is provided in large-sized close type kneaders aiming the improvement of productivity, and various performances of kneading rotors having vane are improved. As there are many cases in which a large amount of kneading material having high hardness and abrasiveness is provided, there is a need of overcoming the problem of increasing the life length of protective tube without compromising the heat sensitivity of the temperature detection end. Further, in these cases, a mechanical load applied on the temperature detection end of the thermocouple temperature detector is substantially increased, and in addition to that, the load is more frequently applied on the protruding section of the temperature detection end in the front and back direction and in the right and left direction. As a result, the life length of the existing thermocouple temperature detectors tends to be substantially reduced.
As described above, since a high speed and excessive energy is applied on the kneading material, it is inevitable that a load applied on the temperature detection end is increased compared with the conventional example. Since the temperature of the kneading material rapidly increases, the temperature needs to be precisely measured in real time. However, as the strength of protective tube is improved, the heat capacity is also increased, and this makes it difficult to perform real time measurement. Therefore, how the shape of protective tube is formed and how it is mounted on the kneading tank are important for performing precise temperature measurement while preventing bending or breaking of the detection end of the thermocouple temperature detector.